It is known that milk is emulsified, in order to obtain cappuccinos and the like, by immersing the steam dispensing spout, for example of a coffee machine, in the milk contained in a vessel.
The steam injected into the milk heats it and simultaneously entraps air particles which produce the typical froth of cappuccinos.
Obtainment of an abundant froth is thus entrusted to the skill of the operator, since if the spout were to be insufficiently immersed in the milk the steam which leaves the spout would produce dangerous spurts without allowing the forming of froth; on the other hand, excessive immersion of the spout in the milk would cause excessive heating thereof, causing any emulsion to flop and at the same time preventing the entrapment in the milk of the air particles required to form the froth.
Furthermore, the high temperature reached by the steam delivery spout, since the spout is usually made of metal, burns the milk on its internal and external surfaces, thus forcing the operator to clean it frequently both for the sake of hygiene and to avoid the partial or total obstruction of its channel.